1. Field of the Invention
The present invention relates to an air bag apparatus which protects the occupant of a motor vehicle in the event of a side collision thereof in such a way that an air bag is deployed into the passenger compartment of the vehicle from an air bag module arranged inside of a seat back of a seat of the vehicle.
2. Description of the Related Art
An air bag apparatus for coping with the side collision of a motor vehicle is known. For example, U.S. Pat. No. 5,498,030 discloses such an air bag apparatus. In the prior art apparatus shown in that patent, an air bag module is arranged inside of a seat back by being enclosed within a pouch made of fabric. An air bag, included in the air bag module, breaks through a sewn portion of a covering member of the seat back by means of the inflating pressure thereof, and the air bag is deployed into the passenger compartment of the vehicle through an opening formed in the sewn portion.
Meanwhile, a force, caused by an occupant of the vehicle leaning his/her back against the seat back, is transmitted to the air bag module through the covering member and pad of the seat back. In this regard, the mere enclosure of the air bag module in the fabric pouch is not sufficiently reliable to protect the inflator, the air bag, the harness, etc., which form the air bag module from the force of the occupant's back against the seat back. In a case where the air bag module is housed within a module case formed of a hard material such as synthetic resin, and where the air bag is inflated by opening or lifting a lid which is provided in the module case so as to be capable of opening, the air bag module is more likely to be protected. Moreover, in this case, the air bag can be reliably deployed in a predetermined direction through an open space formed by the opening of the lid.
However, when any one of the door and center pillar between two doors of the vehicle is deformed toward the interior of the vehicle passenger compartment by the side collision, and has come into contact with the side surface of the seat back, the lid of the module case will be pressed upon by a force and made unopenable by the pressing force of the contacting part, and the air bag will not smoothly inflate.
Besides, when the sewn portion of the covering member is torn by the inflation of the air bag, the inflating pressure of the air bag needs to be concentrated on the sewn portion. Herein, unless the covering member is fixed in place, the shift or elongation deformation of the covering member will make it impossible to concentrate the pressure on the sewn portion so that the sewn portion cannot be torn reliably every time. Further, in a case where the covering member is constructed of a trim cover located on an outer side thereof, a wadding cover located on an inner side thereof and a wadding sandwiched in between the trim cover and the wadding cover, a wadding cover, which is formed of a material softer than the material of the trim cover as is the case in the prior art, poses the problem that only the wadding cover is readily deformed or torn by the inflating pressure of the air bag so that the pressure cannot be concentrated on the sewn portion. Also, when the trim cover is formed of a material which easily elongates, the same problem that the pressure cannot be concentrated on the sewn portion occurs.